(1) Field of the Invention
This invention relates to rod-pumped producing oil wells. More specifically the invention relates to wear impeding sucker rod guides. Those having ordinary skill in the art are oil field workers responsible for repair and maintenance of producing oil wells, and oil company mechanical management associated with the operation of these wells.
(2) Description of the Related Art
One of several methods for removing crude oil from beneath the ground employs a pump-jack located on the surface of the ground above an oil reservoir. The pump-jack is connected to a down-hole pump at the bottom of a producing oil well using a sucker rod string. The sucker rod string comprises many sucker rods, each rod connected end-to-end by a coupling. The entire rod string extends down into a tubing string that is contained within well casing. The well casing is permanently installed during the drilling of the oil well. The tubing string serves as a conduit for produced fluid.
Cyclical upward and downward motion of the pump-jack is communicated to a down-hole pump located at the lower end of the tubing string. In response, the pump forces produced fluid collected at the bottom of the well up the tubing string to the ground's surface. The fluid acts as a lubricating bath for the rod string. Lubrication is derived from the fluid because it is a mixture including crude oil and water. Ultimately, the fluid is then stored near the well until it is removed for refining.
The sucker rod string reciprocates inside the tubing string as a result of the upward and downward motion of the pump-jack to which the rod string is fastened. Due to deflections of both the tubing string and the rod string, contact may occur between the two components. Even though the lubricating bath of crude oil is present, wear is incurred by the rod string when contact is made with the tubing string. The rod couplings typically have the largest outer diameter of the different components of the rod string and therefore incur the most wear.
Included in the crude oil are dissolved salts, gases, and undissolved minerals. When these come between the rods, couplings, and tubing, abrasion and corrosion occur. Through time, abrasion and corrosion will lead to parting of the rod string and holes in the tubing string When a hole develops in a tubing string, pressure inside the tubing string will be lost. Crude oil will then be pumped into the annulus created between the tubing and casing, instead of to the surface for collection.
When a sucker rod parts, a rod coupling breaks, or holes are created in the tubing string, either or both of the sucker rods or tubing must be pulled from the well and inspected for damage. Defective rods and tubing must be replaced. The resultant pulling unit costs and down-time of the well are a great expense to the pumping unit operator. For these reasons, methods for reducing or eliminating these periods of down-time are of great benefit to the owners.
A well known method of preventing wear to the rods and tubing string is the use of sucker rod guides, also known as centralizers. Rod guides have a greater outer diameter than all other parts of the rod string. As such, the guides act as a sacrificial and protective element by retarding wear and by incurring any wear that does occur.
The rod guides are normally attached at three or four locations on each sucker rod but may be used in as many as six locations per rod or as few as one per rod. As such, the guides act as a sacrificial and protective buffer between the rod string and the tubing string. Wear occurs to the guide as it protects the rod string and results in a reduction of the guide's protective thickness.
The wearing effect suffered by the guides will cause the guides to eventually have an outer diameter similar to that of other parts of the rod string. Then guides will not buffer contacts between the rod string and the tubing string. These types of rod guides must be periodically replaced.
Sucker rod guides having two different methods of installation are currently available; those that are manually fastened about the sucker rod and those that are injection molded in place about the sucker rod. Both type of guides are formed from wear resistant plastic materials. These materials currently include: polyphenylene sulfide, NYLON, polyethylene, polypropylene, polycarbonate, polyester and acetal. The manually installed rod guides permit installation in the field. The injection molded rod guides are installed in a factory before the sucker rods are transported to the well site.
There are several known designs of existing rod guides. One version comprises a solid ring-shaped guide that is fixed about the sucker rod. The guide extends outwardly away from the exterior surface of the sucker rod toward the tubing string. Fluid flow channels through the body of the guide are often provided. Otherwise, the guide's thickness significantly impedes the upward flow of produced fluid.
Another known version of the rod guide includes a cylindrically shaped guide similar to that described in the paragraph above. The circumferential surface of this guide is fluted so that oil passes through the depressions of the scalloped surface. The ridges between each depression provide the greatest outer diameter of the guide and serve as the buffering contact surface against the tubing string.
Another design includes wheels along the circumferential surface of a cylindrical guide. The wheels are oriented so that they roll as the rod string reciprocates within the tubing string in the event of contact between the wheels and the tubing string.
A drawback of the first two described designs is that contact between the guide and the tubing string does occur and these guides eventually wear down and must be replaced. Additionally, minerals, paraffins, and other elements contained in the produced oil may adhere to the guides. These deposits may cause clogging to the channels through which it is intended for the produced oil to flow. The wheeled design may also become fouled with mineral scale and paraffin deposits so that the wheels no longer rotate and begin to wear.
Two additional designs are illustrated in FIGS. 2 and 3 of the included drawings. FIG. 2 shows a known style rod guide 21 that is used in the oil field today. The general shape of the guide 21 is cylindrical with ridges about the exterior surface. The long axis of each ridge is parallel to the long axis of sucker rod 12. There are depressions between each ridge that act as channels along the guide for the produced fluid 24 as it is pumped up tubing string 16. An example of this configuration is shown in U.S. Pat. No. 4,343,518 to Pourchot.
FIG. 3 shows another known sucker rod guide 23 that is also presently used in the oil field. The outer diameter of the rod guide 23 in this style is smaller than the outer diameter of the guide 21 found in FIG. 2. As can be seen in FIG. 3, the guide's 23 outer diameter is sufficiently large to prevent contact between the rod string and the tubing string, but it is small enough to allow fluid to pass by the guide. Each guide shown in FIGS. 2 and 3 protect the sucker rod and allows the produced fluid to flow upwards in the tubing string. The common detriment of both guides is that each incurs deteriorative wear and must be periodically replaced.
Before this application was filed, the applicant was aware of these additional United States Patents:
2,166,116 BETTIS PA1 4,043,410 BENNET PA1 4,690,229 RANEY.
BENNETT shows an anti-sticking tool for drilling pipe designed to redirect drilling fluid so that said fluid prevents the drill string from sticking to the well bore.
RANEY shows a radially stabilized drill bit that has means for stabilizing the drill bit as the bit is rotating while making hole.
BETTIS shows a well casing protector that has grooves. Said grooves concurrently act as impellers and channels for drilling fluid. The protector's impelling action throws drilling fluid outwardly against the casing from the protector which is attached to the drilling string.
The above three referenced devices are all used in conjunction with a drilling string during the digging of a well, not with the rod string of a producing oil well.